Split truncated cone-antenna



NOV. 10, 1953 p. KEELER 2,659,002

SPLIT TRUNCATED CONE ANTENNA Filed March 29, 1946' INVENTOR PRICE M. KEELER ATTORNEY "Patented Nov. 10, 1953 ease-m issue "eaten Price Keeler, V Hempstead,

"the United- States 'of Amei-iea its reiifienteii by the-secretary of-War Application Macias, 194tf'seiiai "ms-651.933 11 Claims. wuzso se) invention relate r'generan to el ctrical apparatus'and "more particularly" toaradio ire- ('1' hey antenna "whose horizontal pattern is relatively 'free of nulls'and is nearly "circular-in shape. Y 7

Fo'r certainpur'po'se's it is desirable to'radiate radio frequency energy equallyinall directions. 'I'li'at isto'say, although there are advantages in antenna 'directivity for certain purposes, for other purposes it is quite undesirable. It is sometimes desirable that "substantialy equal signal strength be' emanated 'r-roma radiating element in every direction. For 'e'iianiple, it mightibe e'iipedie'ntfor a hovering aircraftto play the part of a broadcating station. Such -a plane in cruising-about, wouid have" frequently to change directionin order' 'not to lay away from the zone of its'oper'ation. 'If its antenna "system; were directive, movements "of the plane -tifould' be felt in some receivers as changes in "signal strength.

Ontype of antenna, which might seem to have the'proper form of radiatiOnpattern, is a quarter wavelength dipole lprotrudirig from "the bottom of 'theair'craft and pointing toward the gound. It certainly would'radiate energy in all directions in the horizontal plane. However, since 'thepolarization of this antenna is vertical, its use might not always beappropriat'e'ii the antenna systems of most ret'qeivers, associated with -such a broadcasting system, were horizontally polarized. p

It is a r-object of this invention to provide an antenna having :a substantially circular radiation pattern in a plane thatmay -beconsidered horizontal andis, -in -fact,a plane perpendicular to the axis of themain elementof this-antenna. Itis also an object of this invention that this antenna offer a favorable input impedance --for eflicient power transfer from ordinary feed lines. It is a further object of this inventionthatthis antenna be horizontally polarized. -It is a further object of this invention that'this antenna be adaptablefor operation over a relatively wide band of -frequencies.

Generally, this invention comprises a structiire in the form of a truncated coneconductive over at least its outer surfaceexcept for what may be a non-conductive strip "running the length of the structure'with itsaxis substantially c'oplanar with the axis of the tube. The width of this strip is small by comparison with its length. The interruption inth'e continuity of conductivity of the outer surface may take the form of aphysical split or :slit cut from the conical structure (in the location described above) and particularly so if solid sheet metal is "usdt'o farm tiiis t'fiiutive split conical structure is ied with radiofr'tiueney energy ,iapplie'd 'from "suitable transmission line iriea'ns ft'o selected points "on "ea th side 'of the slit and f communieated by, waybi the edges of the slit to -substam a1y a11 of said iconductiv' e surface; said easnaucti've serrate l radiates said electromagnetic energywithits electric vector polarized in a "pl'ane, 'o'r fplaneg substantially perpendicular to the axis of -"-said *cbnical "ele f Otlier objects, features, seq-adva ages of; this invention war-suggest; ern'selvs-tothose skilled in the art and will be'cemefappaent from the following description or "the in ntion taken in connection with the single figureor "tue aecom flam g w 1: 1: i

' The figure is' 'an istmetric view annemtear ment oi this invention.

Referring now to the *arawmgthe "split truncated eerie l is composed bf thin -s'ht metal. I 7 It "might be "termed by cutting "sheet metal along "two jean/ed fines. I drawn apprdxi mately as parallel segments "of two concentric circles, andalon"g two radii, each one 'drawn'as a radius "common "to said two circles and to interse'ct said two curved lines near "their respective "ends (a jpattern jcomonly employed in making simple lamp shades), and by bending said sheet metal, so cut out, into substantially the form fof atrunca'td "eons, until the two straight edges idrmedby 'said radii nearly touch and farm, between "them, a narrow slit the aids of which' is coplanarwith the axis of said cone. The larger end of thus truncated cone abuts against, and is attached to, a substantially fiat element 2 which may be another piece of sheet metal, specially selected for the purpose, or may be, in effect, furnished by some conducting portion oi the bottom surface of the aircraft on which this antenna may be installed. Flat element 2 serves an obvious mechanical function inadding to the rigidity of truncated cone l Besides thisjitaffects the-overall behavior of the radiating element by'serving as a ground plan Coaxial transmission line3, having -an outer conductor 4 and-an-inner conductor 5, may be'led totheinside oftrunoated cone I by comi-ng through a-hole, infiat element 2, situated near an edge =of-slit 6. -Whenthe feed-line is installed in this manner, itmay-be' ledalong said edge to-its opposite end "(tothe place-wherecone l remains open-as show-n the figure) Outer conductor 4 may bemechanically and electrically connected toone edge of-slit 6 either'along the full length of the slit or at its above described end. In the embodiment, and patricularly as shown in the figure, this connection is made at the end of outer conductor 4 and is made between outer conductor 4 and the end of one edge of the slit. It may be made by soldering or brazing or by any other suitable conventional means. In the figure this connection is shown as'a solid inked-in area at a point of contact between the connected parts. Inner conductor 5 extends beyond outer conductor 4, at this point, and is bent over and electrically joined to the opposite edge of the end of slit 6. Shorting bar 1 is adapted to slide between, and to have good electrical contact with, the edges of slit 6, thus short circuiting those edges at any point where it is positioned. Conventional types of spring contactors may be used and incorporated into shorting bar 1, or it may be fashioned as a clampable element which can, at will, be mechanically loosened, positioned, and retig'htened. I

The length or slit' 6 should be' somewhat greater than one-half of one wavelength corresponding to the lowest intended operating frequency. While thevelocity of propagation along slit t may sometimes be exactly equal to the speedof light, it may vary so as either to be somewhat' les's or somewhat greater than that velocity. Therefore, in most cases, this dimension will be somewhat different physically than electrically. Generous proportioning as to the length of the slit may be advisable in order to give due allowance to this fact. Then, in actual operation, the shorting bar may be set as a point on the slit which is distant from the feed point by an exact effective half wavelength even if the velocity of propagation along the slit is greater than the speed of light. r

- It has been found empirically that the approximate circumference of the conical element should be near to one whole wavelength in space. It is likely that reactance loading effects inherent in this metallic structure (which can be looked upon as a single turn of a wide strip of metal) may afiect the electrical length measured around the outside of the tube, between the edges of the slit, sothat the effective electrical length is really quite difierent than the physical measurement. However, that may be, it has been determined as a fact that in the case of a cylindrical structure the physical size of the circumference should be about equal to of the longest wavelength in space. Since the antenna is in the form of a truncated cone, that size would be correct for the circumference which the outer surface of said cone would form on an intersecting plane perpendicular to the axis of said cone and lying about midway between its ends. Where the truncated cone is proportioned in this way, the device becomes adjustable over a broader frequency hand than if a cylindrical shape were used. For as the shorting element is moved close to the feed point, to adjust the length of the slit to a high operating frequency, then the circumierence'of the used portion of the radiator (which might have been correct for a lower frequency) would probably be incorrect and would be too large. Instead, the average circumference of the used portion of the radiator becomes progressively smaller at the same time that the distance along the slit is reduced.

With proper adjustment of shorting bar I this radiating element presents a good impedance match to a low impedance feed line.

The foregoing portion of this disclosure has indicated some of the controlling facts about the structure of this antenna. The following portion is a suggested explanation as to some of the principles of its operation. The R. F. potential difference between the conductors of the feed line when applied between the open ends of the slit causes a wave to travel along it toward shorting bar I. This wave is reflected by the shorting bar and, since the attenuation of the forward and reflected waves is not very great, a standing wave is formed along the slit. If the position of shorting bar I is adjusted properly, the standin wave will include one whole voltage loop with voltage nulls occurring at the feed point and the shorting bar. When the slit is tuned to resonance, in this way, it offers a pure resistance load to the feed line, and the value of this load is a low one.

The phases of the R. F. potentials at different points along the slit will be practically the same though the potential differences at these points will vary according to the standing wave ratio.

The potential differences existing between the two edges of the slit will cause R. F. currents to flow around the conductive outer surface of the conical element and will cause an electric field to be set up whose lines of force will be roughly parallel to the paths of these currents. As a result, the entire outer surface will radiate R. F. energy which is polarized in a plane perpendicular to the axis of the conical element.

The cone acts as though it consisted of a number of individual loops piled up coaxially and energized in phase.

By reference to well known facts about the behavior of closed loops it could be inferred that the horizontal radiation pattern of this device, if its polarization be termed horizontal for purposes of convenience, would be rather nondirectional.

It has been observed by actual experiment,

that the radiation emitted by this antenna is distributed in those planes which include the axis of the tubular element so as to form radiation patterns describing the form of a figure 8 lying on its side, that is with its nulls being along the axis of the cylinder. The radiation emitted in planes at right angles to the axis (the radiation herein referred to as horizontal) forms patterns which vary with changes in the frequency applied to the antenna, without readjustment, but are generally cardiodal at higher frequencies and nearly oval at lower frequencies. However, at

v any frequency within its operating range this antenna has a horizontal pattern which is no-' ticeably nondirectional and has no pronounced nulls. 'The radiation is, however, a little greater in a direction out of the slit from the axis than in the opposite direction or in directions toward either side.

It is obvious that the horizontal radiation pattern could be made even more circular if the slit were made to follow a helical path around the surface of the conical structure instead of a face would emit certain radiations out at phase.

with? other radiations: and their wouldz notaadd up; to]. products-the kindaoi: patternss-ina tha zontal-i and. vertical planes. described. iabqver. However; there. are; methodswell. known; "in prior art; for: meetingthis; problem... For: example the:

slit mauld. be fedi at a: plurality of. pointslsoi as; to

betexcitedsima plurality of sectionsseaclr of. which: could individually" be. limited to.- aqsingle eiilectiye halitwavelength and where: the; feed lines; would be: of. such; unequal-.lengthsias. tocause: said, sections; oii said slit to beexcited. in phase Itwill. be seen. that the antenna herein set forth will radiate energy horizontally polarized andzwilt do; so without: obj ectionablynpronounced directivityin the horizontal plane and without marked nulls in its horizontal radiation pattern; that it" presents a favorable input impedance? that it canbe made adjustable ever a relatively broadband ofoperating frequencies.

-It is obvious that agreat many minor variations in the details of designand of materials used in constructing antennasof" this type could be embodied in it without departing from the basic principles of the-invention.

Accordingly all suchdeviations are claimed which fall" fairly within the: spiritand scope of theinvention as identified in the hereinafter appended claims,

What is claimedis: 1

1. A broad band. antenna. including a hollow metallic truncated cone having a length greater than one-hall." ofone wavelength;corresponding to the lowest operating'irequency' and an average circumference greater than a wavelength corresponding to the lowest operating frequency with a narrow slit whose axis is coplanar with the axis of said cone extending the full length of said cone, a metallic sheet reflector oriented perpendicular to the axis of said cone electrically contacting the periphery of said cone at its larger base, a coaxial transmission line a portion of which is mounted in said cone through a hole in said reflector with the outer conductor of the portion of said line contained by said cone parallel to the slit in said cone and electrically connected along its entire length to said cone near the slit in said cone and with said outer conductor terminated at the smaller base of said cone and with the inner conductor of said line extending beyond said outer conductor and terminated in electrical contact with said cone at the opposite edge of the slit in said cone at the smaller base of said cone and an adjustable shorting bar electrically connecting opposite edges of said cone resulting from the slit in said cone.

2. A broad band antenna with a plane polarized substantially circular response pattern in a plane perpendicular to its axis including a conductive sheet in the form of a truncated cone with a slit coplanar to the axis of the hollow cone, a conductive sheet reflector oriented perpendicular to the axis of said cone electrically connected to the larger base of said cone, a coaxial transmission line a portoin of which is mounted in said cone through a hole in said reflector with the outer conductor of said line terminated in electrical contact with the smaller base of said cone near one side of the slit in said cone and with the inner conductor of said line terminated in electrical contact with the smaller base of said cone near the other side of the slit in said cone and a shortalongthalengthzoiesaidi, slit: whereby-said: antemia: has; a. lovwzinpntuhnw iiedmes.

- a abroadibandantennawithia planepoiarizea:

i substantiailyscircular;responseapattemima plana peniendicular. to; its axis; including a; truncated? substantiallyv'conical radiator with; a; longitudi e nal slit. along the: full? length-l of said. radiatoni. a; sheet: reflector oriented; perpendicular toftheeaxiss off said. radiatozrin electrical. contact-with; am. end? of. said radiator; a: coaxiali transmission a. portion of which is; mounted said. radiator through a holein; said: reflector with. the outer conductor of said line in; electrical contact: with said radiation along: one: edge: ofv thee slit; in. said; radiator and; with said; outer conductor tel-mi:- nated; at the end of: said radiator opposite: saidi reflector with the. inner conductor of said: lineaextending beyond said outer conductor and. connected: to" said v radiator at the other: edge; of: the: slit in said radiator and. a. shorting; barxcone-e nected. to: said radiator across the: slit said; radiator and adjustable along the; length of said. sliti whereby the; input. imp edance: of said. antenna is or a low value.

4e Abroadzbandantennawithaplanespolarized substantially" circular response. pattern; in a. plane perpendicular to: its axis including; a. truncated substantially conical. radiator with: a: longitudinal: slit; along the: full length of. said. radiatonna reflector. at; one; end of: said radiator.- in a; plane; perpendicular; to: the; axis; of; said radiator; acoaxial transmission: linewith its; inner conduc-= tor connected to said radiator near-art edge. of: the'slit in saidiv radiator; and with its outer cone-, ductor connected to said radiator near an opposite edge of the slit in said radiator and a shorting bar connected to said radiator across said slit and adjustable along the length of said slit whereby the input impedance of said antenna is of a low value.

5. A broad band antenna with a plane polarized substantially circular response pattern in a plane perpendiculr to its axis, said antenna comprising a hollow metallic body having an outer radiating surface substantially in the form of a truncated cone with a substantially straight slit in its periphery and a transmission line comprising two conductors with one of said conductors connected to said body near one edge of said slit and with the other of said conductors connected to said body at a point on the opposite edge of the slit in said body.

6. A broad band antenna with a plane polarized substantially circular response pattern in a plane perpendiculr to its axis, said antenna comprising a hollow metallic body having an outer radiating surface substantially in the form of a truncated cone and having a longitudinal slit, a transmission line connected to said body across the slit in said body, and a shorting bar connected to said body solely across said slit, said shorting bar being adjustable along the length of said slit.

7. A broad band antenna with a plane polarized substantially circular response pattern in a plane perpendiculr to its axis, said antenna comprising a hollow metallic body having an outer radiating surface substantially in the form or a truncated cone and having a longitudinal slit therein, ,means coupled to said body across said slit for applying high frequency energy thereto, and tuning means coupled to said body across said slit to tune said slit.

8. A broad band antenna with a plane polarized in b co ec d t a @0118 across the slit in substantially circular response pattern in a plane perpendicular to its axis comprising a truncated substantially conical hollow radiator with a longitudinal slit, the efiective electrical peripheral measurement of said conical radiator at substantially the center thereof being approximately an electrical wavelength at the mid-operating-frequency, means coupled to said radiator across said slit for applying high frequency energy thereto, and short-circuiting means coupled to said radiator across said slit and longitudinally movable therealong to adjust the effective electrical length of said slit to one-half wavelength.

9. A broad band antenna with a plane polarized substantially circular pattern in a plane perpendicular to its axis comprising a hollow metallic body substantially in the form of a truncated cone and having a longitudinal slit, the effective electrical peripheral length of said body at sub-- stantially the longitudinal center thereof being.

approximately an electrical wavelength at the mid-frequency of said band, and energy transmission means coupled to said body on opposite.

sides of said slit.

10. A broad band antenna with a plane polarized substantially circular pattern in a plane perpendicular to its axis comprising a hollow metallic body in the form of a truncated cone and having a longitudinally slit, the efiective length of said slit being at least approximately equal to a half wavelength at the lowest frequency in said band, the effective electrical peripheral length of said body at substantially the center thereof being approximately an electrical wavelength at the mid-frequency of said band, energy transmission means coupled across said slit for applying 8. high frequency energy thereto, and means to tune said slit. l

11. A broad band antenna having a substantially circular pattern plane polarized in a plane perpendicular to its axis, said antenna comprising a hollow metallic body having an outer radiating surface substantially in the form of a truncated cone and having a longitudinally slit therein, the effective length of said slit being at least approximately equal to a half wavelength at the lowest frequency in said band, and energy transmission means coupled to said body on opposite sides of said slit for applying energy thereto.

PRICE M. KEELER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,218,741 Buschbeck Oct. 22, 1940 2,234,293 Usselman Mar. 11, 1941 2,238,770 Blumlein Apr. 15, 1941 2,243,136 Trevor May 27, 1941 2,368,663 Kandoian Feb. 6, 1945 2,369,556 Garnet Feb. 13, 1945 2,414,266 Lindenblad Jan. 14, 1947 2,479,209 Chu Aug. 16, 1949 2,513,007 Darling June 27, 1950- 2,521,844 Gordy Sept. 12, 1950 OTHER REFERENCES Radio, December 1945, FM-FAX skyrocket antenna, pages 38, 58, and 59.

Electronic Industries, January 1946, Experimental FM antenna," page 126. 

